Preparation

Heat the olive oil and butter in a large saucepan.Add onions and potatoes with a good pinch of salt.Cover and cook 10 mins.Stirring occasionally.Add zucchini, corn, cumin, and garlic.Cook 2 mins.Add stock, season and bring to the boil.Reduce heat and simmer 10 mins or until the potatoes and corn are tender.Set aside to cool a little.Transfer one third of the soup and all of the basil to a food processor.Blend until smooth.Return to saucepan with other soup.

To serve:Reheat soup and season if necessary.Ladle into warm bowls.Top with a spoonful of yoghurt extra basil and a drizzle of olive oil.